The present invention relates to a method of and apparatus for, controlling the flow rate of air intake of an internal combustion engine, particularly as it relates to an air intake control method during the idling condition.
There is known a method of controlling the air intake of an internal combustion engine when a throttle valve disposed in an intake passage is at the fully closed position. According to this conventional method, the flow rate of intake air, when the throttle valve is fully closed, is controlled by adjusting the bypassed section of a flow passage by means of a control valve disposed in an air bypass passage which communicates the intake passage at a position located upstream of the throttle valve with the intake passage at a position located downstream of the throttle valve. Such an air intake control method is usually employed for controlling the idling rotational speed of the engine. The idling rotational speed can be controlled by a closed loop if the bypass control valve is adjusted to control the flow rate of the air sucked into the engine through the bypass passage so that the detected actual rotational speed of the engine becomes equal to the reference rotational speed which corresponds to a desired idling rotational speed.
According to the conventional intake air control method, the reference rotational speed is predetermined by a desired rotational speed which is changed depending upon the warmed up condition of the engine and upon the load condition of the engine but is not changed depending upon whether the engine is in the starting condition or not. Therefore, according to the conventional method, the following problems often occur.
(1) The reference rotational speed becomes quite the same value when the temperature of the engine which is started from cold reaches, for example, 60.degree. C. and when the engine which has been completely warmed up is temporarily stalled and is soon re-started again while the temperature is 60.degree. C. In the latter case, in general, there is no need to set the reference rotational speed high, but the reference rotational speed should rather be set low to reduce the consumption of fuel. In the former case, on the other hand, the reference rotational speed should be set high to improve the starting performance and the operation feeling when the engine is being started. Therefore, if the reference rotational speed is set so as to satisfy the latter operation, the actual rotational speed becomes too low and the operation feeling is deteriorated during the former operation. Further, if the reference rotational speed is set so as to satisfy the former operation, the actual rotational speed becomes too high, the operation feeling is deteriorated, and fuel is consumed in large amounts during the latter operation.
(2) Immediately after starting, the actual rotational speed of the engine generally rises quickly. If the reference rotational speed is controlled in an ordinary manner under such a condition, the control system is excessively corrected, and the actual rotational speed after ones controlled develops overshooting and hunting.